1. Field of the Invention
This invention relates to stable plasticized PVC compositions, and, more particularly, to stable alkyl pyrrolidone plasticized PVC compositions comprising an organic phosphite ester stabilizer present in an amount sufficient to provide long term high temperature stability and better color and clarity. The present invention also relates to alkyl pyrrolidone plasticized PVC compositions which are free of heavy metal and solvent, thus exhibiting reduced volatile organic compounds (VOC) emissions. The present invention also relates to the use of stable alkyl pyrrolidone plasticized PVC compositions in medical tubing, roofing membranes, vinyl flooring, refrigerator gaskets, paints, adhesives, textile auxiliaries, film coating, fabric, wall paper coatings, etc.
2. Description of the Prior Art
U.S. application Pub. No. US 20070112104 A1 describes a new class of alkyl pyrrolidone plasticizers which provide long term plastification to PVC so as to impart flexibility, softness, extensibility and or/lower melting temperature to PVC compositions. The present invention provides improved stable alkyl pyrrolidone plasticized PVC having excellent early color performance while maintaining good processing heat stability at higher temperatures.
Poly(vinyl chloride), hereafter referred to as PVC, is extensively used in many applications. In use, PVC is plasticized to permit it to be processed into a flexible material. In addition, other additives such as thermal stabilizers, lubricants, pigments, fillers, impact modifiers, and flame retardants are generally employed to produce PVC compositions having desired properties.
It is known in the prior art that plasticization of PVC makes it useful for various applications, however during the plasticization process, due to high temperature, PVC tends to degrade by various processes like dehydrochlorination, auto-oxidation, mechano-chemical chain scission, cross linking of macromolecules and condensation reactions. Yellow discoloration, resulting from the formation of conjugated polyene sequences of 5 to 30 double bonds of the polymer, indicates the start of primary degradation process, which on subsequent secondary reaction results in cross linking or the cleaving of the polymer chain. These changes lead to altered physio-mechanical and rheological properties of PVC.
A number of stabilizing systems have been proposed to reduce the degradation and thus maintain early color and clarity. The chief purpose of a heat stabilizer is to prevent discoloration during the processing of the PVC at high temperature. Degradation of PVC polymer begins with the evolution of hydrogen chloride at about 100° C. and accelerates exponentially at higher temperatures. Thus the heat stabilizer ideally must inhibit or prevent the dehydrochlorination reaction that is the primary process in degradation.
Typically various stabilizers have been used to tackle such situations. The most common, well established and conventionally used heat stabilizers are tin based organotin compounds such as organotin mercaptides, lead based stabilizers and the mixed metal type stabilizers containing barium/zinc/cadmium combinations. However, these stabilizers are associated with many drawbacks such as heavy metal toxicity, environmental safety concerns coupled with VOC emissions, and the strong and repulsive odor linked with mercaptides. Additionally, high cost is also linked with metal based stabilizers.
Thus it is very much desired to have a cost effective compatible stabilizer, which is free of the above mentioned shortcomings. More particularly, it is desired to have sufficiently flexible plasticized PVC having excellent heat stability at higher temperatures for sufficiently longer duration.
The prior art disclosing attempts to solve the above mentioned problems are exemplified in U.S. Pat. Nos. 5,575,951; 5,672,646; 5,656,202; 5,985,958; and 5,859,103.
U.S. Pat. No. 6,667,357 discloses organic thiol compounds which can be utilized to plasticize and stabilize halogen-containing polymer compositions against deterioration and color change that typically occurs during the processing of PVC polymer.
U.S. Pat. No. 7,320,764, assigned to Dover Chemical Corporation, discloses the Phosbooster® stabilizer series. Blends of phosphite esters with zinc for improving the performance and reducing the heavy metal content of PVC compositions are described.